A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
A chuck may be used as part of a patterning device stage to hold and position the patterning device, on a corresponding support of the patterning device stage. Chucks are also used as part of a substrate stage to hold and position the substrate, on a corresponding table of the substrate stage. As the patterns to be transferred from the patterning device towards the substrate grow increasingly smaller, the demands on the various components of the lithographic apparatus increase. Specifically, the chuck positioning tolerances decrease, which has a direct impact on the positioning control systems for the stages.
To propel and position an object, like for example a patterning device, weighing no more than 0.5 kilograms, typically a chuck of about 10-15 kilograms is desired. For such a chuck, it is desirable to use a stage weighing about one thousand kilograms to accurately propel and position the patterning device. In order to achieve a high throughput at a reasonable cost, the weight of the chuck may be reduce. For example, the chuck may be constructed as a glass block having a box structure with ribs inside. The obtained lightweight chuck enables lighter components across the entire stage, significantly reducing costs and increasing throughput.
However, in general, such ultra-light weight structures with high natural frequencies contain very poor damping behaviour. This poor damping inhibits optimum high stage servo bandwidths.